Which of the following is the least profitable investment for a candy shop that earns $1 profit per pound of candy?

a. worker at $10 per hour, producing eight pounds of candy per hour

b. worker at $12 per hour, producing 16 pounds of candy per hour

c. machine with $5 per hour operating cost, producing 10 pounds of candy per hour

d. machine with $8 per hour operating cost, producing 14 pounds of candy per hour